Method for explosive bonding of metals

ABSTRACT

A strip of low detonation velocity explosive overlies spaced overlapping portions of metal bodies to be bonded and a narrow cord of high detonation velocity explosive extends in the direction of the weld along one edge of the low detonation velocity strip such that initial ignition of the high detonation velocity explosive cord creates a detonation front which moves across the weld at an angle whose tangent is the ratio of the detonation velocities of the two explosives to prevent deformation of weld geometry ahead of detonation.

ilmiiefl States P310111 91 1111 3,732,612 Simon 1451 May 15, 1973 54 METHOD FOR EXPLOSIVE BONDING 3,281,930 11/1966 Fordham ..29 470.2 ux

0F METALS 3,455,017 7/1969 Zondog ....29 470.2 ux Inventor: Wayne E- simon, g e Co o 1126,858 4/1970 Chudylk ..29/4702 UX [73] Assignee: Martin Marietta Corporation, New Primary Examiner-J. Spencer Overholser York, N.Y. Assistant Examiner-Ronald J. Shore J 2 Attorney- L. DeArment Appl. No.: 149,287

[52] US. Cl ..29/470.1

[51] Int. Cl. ..B23k 21/00 [58] Field of Search ..29/470.1, 421 E, 29/486, 497.5

[56] References Cited UNITED STATES PATENTS 3,258,841 7/1966 Popoff ..29/470.2 X

3,261,088 7/1966 Holtzman .....29/470.2 UX

3,263,324 8/1966 Popoff ..29/470.2 UX

[57] ABSTRACT A strip of low detonation velocity explosive overlies spaced overlapping portions of metal bodies to be bonded and a narrow cord of high detonation velocity explosive extends in the direction of the weld along one edge of the low detonation velocity strip such that initial ignition of the high detonation velocity explosive cord creates a detonation front which moves across the weld at an angle whose tangent is the ratio of the detonation velocities of the two explosives to prevent deformation of weld geometry ahead of detonation.

8 Claims, 5 Drawing Figures BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to explosive bonding of metal bodies and, more particularly, to the welding of thin foils without deformation through the use of properly positioned and aligned low and high detonation velocity explosives with respect to the weld area.

2. Description of the Prior Art Thin metal layers have been explosively bonded together by the employment of an explosive which drives one slightly spaced metal layer toward the other, such that the explosively propelled layer achieves an adequate velocity before impact with the stationary layer to effect mechanical bonding between the same. Most of the prior art explosive bonding processes have employed a single explosive having a detonation velocity less than the velocity of sound in that metal with the higher sonic velocity.

Attempts have been made to employ composite explosives in such explosive bonding process, wherein a portion of the explosive constitutes a low detonation velocity explosive, that is, one which is sub-sonic with respect to the sound speed in the metal having the higher sonic velocity, in conjunction with a high detonation velocity explosive, that is, one which is supersonic with respect to the sound speed in the higher sonic velocity metal. In particular, US. Pat. No. 3,263,324 teaches overlying the outside surface of the metal cladding layer of the part to be bonded with a composite explosive layer comprising at least two planar sections positioned in juxtaposed relationship with at least one of the sections being a first explosive having a detonation velocity between 1,200 meters per second and 80 per cent of the sonic velocity of the metal having the highest sonic velocity in the system, and one section being a second explosive having a detonation velocity higher than that of the first explosive and between 80 per cent and 120 per cent of the sonic velocity of the metal having the highest sonic velocity in the system. Further, ignition of the composite explosive layers is such that detonation is propagated parallel to the plane of the metal cladding layer and such that the second explosive initiates but is not initiated by the first explosive.

In the referred to patent, in a preferred form, an arrangement is provided in which the composite explosive charge is initiated at a point or points along one edge of the assembly, and the two corners or the entire end of the metal cladding layer away from the point or points of initiation is covered with the low velocity explosive. Alternatively, in a rectangular composite explosive layer, the center section comprises the higher velocity explosion and a section around the periphery of the layer comprises lower velocity explosive. In particular, in the referred to patent, the employment of limited area sections of low velocity explosive, especially at the edge of the weld area opposite to and in line with the direction of wave front propagation eliminates unbonded zones and other deleterious conditions such as spalling. Further, the patent employs metal extension pieces at the edges to in effect increase the area of bonding and overcome the problems of edge lag."

SUMMARY OF THE INVENTION The present invention consists in the use of a low detonation velocity explosive in conjunction with a high detonation velocity explosive which is supersonic with respect to sound speed in metal, in which the high detonation velocity explosive which is aligned with the direction of weld has the purpose of igniting the low detonation velocity explosive and lies at one side of the weld area whereby the detonation velocity across the weld is maintained sub-sonic with the attendant favorable welding characteristics, while the detonation ve locity along the weld is supersonic so that deformation of weld geometry ahead of the detonation is prevented.

The method of the present invention achieves more uniform detonation of the low velocity explosive in a composite explosive arrangement, reduced thin-out at the edge of the weld, elimination of edge tearing and makes detonation length independent of weld length. The present invention is especially applicable to weld foils as thin as 0.005 inches, without tearing of the foil due to local non-uniformities in the low detonation velocity explosive. The present invention further eliminates completely the necessity of using metal extension pieces to prolong the weld beyond the edges of the substrate or metal body being bonded, since uniform welding or bonding is achieved throughout the length of the weld area.

Specifically, the method of the present invention comprises supporting two metal bodies in edge overlap, planar spaced position, while covering the edge overlap portion of the upper body with a composite explosive consisting of a low detonation velocity explosive which is sub-sonic with respect to the sound speed of the metal body having the highest sonic velocity in the system, and providing a high detonation velocity explosive which is supersonic with respect to the sound speed of the metal body having the highest sonic velocity in the system along one edge of the first explosive and extending in the weld direction, and initially igniting the high detonation velocity explosive, whereby the simultaneous sub-sonic detonation occurs across the weld and supersonic detonation along the weld creates a detonation front moving across the weld at an angle whose tangent is the ratio of the detonation velocities of the two explosives to prevent deformation of weld geometry ahead of the detonation.

Preferably, the sub-sonic explosive consists of a rectangular strip which overlies completely the weld area and a supersonic explosive comprises a narrow ribbon lying adjacent the edge of the sub-sonic explosive which runs the length of the weld area. The supersonic explosive ribbon is preferably positioned along the edge of the sub-sonic explosive closest to the edge of the overlapped body. Preferably the high supersonic explosive has a velocity on the order of per cent of the sound speed of the metal body having highest sonic velocity in the system.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of one embodiment of an assembly which exemplifies the explosive bonding method of the present invention.

FIG. 2 is a sectional view of the assembly of FIG. 1 taken about the lines 2-2.

FIG. 3 is a top plan view of the assembly of FIG. I after detonation of the composite explosive and illustrating the detonation wave front during bonding by the method of the present invention.

FIG. 4 is a sectional view of the assembly taken about lines 4-4 of FIG. 3.

FIG. 5 is an end view of the assembly during bonding taken about lines 5-5 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, FIG. 1 illustrates a typical arrangement or assembly allowing for the practice of the method of the present invention. A mandrel comprising a rectangular metal plate or the like acts as a support for overlapped metal sheets or foils 12 and 14 which may be of similar or dissimilar metals and supported upon the mandrel 10 for explosive bonding or welding in the area of overlap. In this respect, metal foil 14 which may constitute aluminum, for instance, terminates at approximately the middle of mandrel 10 in a tapered or inclined edge 16 which underlies an upwardly inclined section 18 of the overlapped metal foil 12 formed of copper, for instance. The inner edge 20 of foil 12 extends beyond the tapered edge 16 of the underlying foil 14. A rectangular block or strip 22 of low detonation velocity explosive extends the complete length of the overlapped foil and essentially overlies the complete area of the inclined section 18 of overlapping foil 12. The low velocity explosive 22 has a detonation velocity which is sub-sonic with respect to sound speed of the metal body having the highest sonic velocity in the system, in this case aluminum foil 14. A high velocity explosive in the form of a thin ribbon or cord 24 extends the length of the low velocity explosive strip 22 and is affixed to the edge of the same adjacent to the inner edge 20 of the overlying metal foil section 18. The high detonation velocity explosive strip 24 has a detonation velocity which is supersonic with respect to the sound speed of the metal body 14, that is, the one having the highest sonic velocity in the system, and preferably a velocity which is on the order of 190 per cent of the sonic velocity of metal 14.

The term sonic velocity as used herein in connection with metals and metallic systems refers to the velocity of the plastic shock wave which forms when a stress which is applied, just exceeds the elastic limit for uni-dimensional compression of the particular metal or metallic system involved. Not only is the section 18 of metal foil 12 in inclined position and overlying the tapered edge 16 of the underlying metal foil 14, but it is spaced therefrom by a distance indicated in FIG. 2 as gap g. This distance may vary, and may in fact be as small as 0.001 inch between the facing surface of the two layers. However, the gap dimension g is normally several times this, although not generally greater than 0.5 inches. The low detonation velocity explosive constitutes in the illustrated embodiment, a rectangular explosive strip, examples of which are explosives sold under the trade designations SWP-2 and SWP-6 by Trojan-U.S. Powder, a Division of Commercial Solvents Corporation of Allentown, Pennsylvania. The SWP-2 explosive has a detonation velocity of on the order of 5,600 feet per second at a density of 0.75 gm/cm, while the SWP-6 explosive has a detonation velocity on the order of 6,100 feet per second at a density of 0.98 gm/cm. In turn, the high detonation velocity explosive 24 in solid cord or ribbon form may, for example, constitute an explosive sold under the trade name Detasheet C by the E. I. Du Pont de Nemours & Company, Inc., covered by U.S. Pat. Nos. 2,999,743, 2,992,087, and 3,311,513, assigned thereto. This high detonation explosive has a detonation velocity on the order of 22,300 feet per second. The low detonation velocity explosive strip in one example of the illustrated embodiment where copper foil is bonded to an aluminum base, has a height of 0.38 inches and a width of 2.25 inches, which corresponds generally to the weld area width W. In conjunction therewith, the ribbon or cord constituting the high detonation velocity explosive 24 is coupled to a conventional blasting cap 26 which, in turn, is ignited through electrical leads 28 to achieve progressive bonding or welding under the method of the present invention.

Referring to FIGS. 3, 4 and 5, the movement of the wave propagation or detonation front F as indicated by the multiple arrows and its effect in achieving a progressive uniform bonding or welding of the overlapping foil sections or portions is graphically illustrated. The detonation velocity across the weld, as indicated by arrow P in FIG. 3, is at right angles to the longitudinal direction of the weld line and is sub-sonic with all the favorable welding characteristics associated with the low detonation velocity. In contrast, the detonation velocity along the weld as indicated by arrow P is supersonic, so that deformation of weld geometry ahead of detonation is prevented. In turn, the detonation front F as illustrated by the multiple arrows moves across the weld at an angle 0 whose tangent is the ratio of the detonation velocities of the two explosives, that is, the ratio of P to P This achieves, as evidenced in sectional views FIGS. 4 and 5, the creation of a weld region R as evidenced by the double headed arrow which moves inwardly from the outer edge 20 of the overlapping layer 18 or thereabouts towards the left hand edge of the low detonation velocity explosive strip 22 remote from the high velocity ribbon or cord 24. The ignition of the low velocity explosive via the high velocity ignition promotes a very uniform detonation of the explosive strip 22 and better control of welding parameters, and thus it becomes possible to weld foils as thin as 0.005 inches without tearing the foil due to local nonuniformities in the low detonation velocity explosive.

Additional advantages lie in the fact that there is a reduction of thin-out at the edge of the weld especially where the high detonation velocity explosive in ribbon form overlies or is adjacent to the edge of the overlapped foil and this arrangement in conjunction with the orientation of the high and low velocity explosive parallel to the longitudinal axis of the weld area eliminates edge tearing while allowing detonation length to be independent of weld length.

The invention is applicable to explosive bonding, particularly seam welding of all metals provided with the required ductility, and it is particularly advantageous for welding metals of relatively low ductility. The method of the present invention is particularly applicable to those cases where a metal foil is used between two primary metals of the weld because of metallurgical incompatibility of the two primary metals.

What is claimed is:

1. A method for explosive bonding of metals comprising:

supporting two metal bodies in edge overlapped, planar spaced position,

covering the edge overlap portion of one body with a composite explosive consisting of a low detonation velocity explosive which is subsonic with respect to sound speed of the metal body having the highest sonic velocity in the system,

positioning a high detonation velocity explosive which is supersonic with respect to the sound speed of the metal body having the highest sonic velocity in the system along one edge of said first explosive body parallel to the longitudinal direction of the weld area,

initially igniting the high detonation velocity explosive to effect simultaneous subsonic detonation across the weld and supersonic detonation in the longitudinal direction of the weld which creates a detonation front which moves across the weld at an angle whose tangent is the ratio of the detonation velocity of the two explosives to bond said bodies at their overlapped interface while preventing deformation of weld geometry ahead of detonation.

2. The explosive bonding method as claimed in claim 1, wherein the supersonic explosive lies along the edge of the overlying metal body.

3. The explosive bonding method as claimed in claim 2, wherein said subsonic explosive comprises a rectangular strip of low detonation velocity explosive which completely covers the overlapped portions of the metal bodies and said high detonation velocity explosive is in cord form and lies along the edge of the strip of low velocity explosive adjacent the edge of the overlapped metal body.

4. The explosive bonding method as claimed in claim 1, wherein said low detonation velocity explosive has a detonation velocity on the order of 5,600 feet per second to 6,100 feet per second and said high detonation velocity explosive has a detonation velocity on the order of 22,300 feet per second to 23,600 feet per second.

5. The explosive bonding method as claimed in claim 3, wherein said low detonation velocity explosive has a detonation velocity on the order of 5,600 feet per second to 6,100 feet per second and said high detonation velocity explosive has a detonation velocity on the order of 22,300 feet per second to 23,600 feet per second.

6. The explosive bonding method as claimed in claim 5, wherein said overlapping metal bodies are on the order of 0.005 inches in thickness and are spaced from each other in the overlap area a distance of 0.030 inches.

7. The explosive bonding method as claimed in claim 11, wherein the detonation velocity of the high velocity explosive is in excess of percent of the sonic velocity in the metal body having the highest sonic velocity in the system.

8. The explosive bonding method as claimed in claim 3, wherein the detonation velocity of the high velocity explosive is in excess of 150 percent of the sonic velocity in the metal body having the highest sonic velocity in the system. 

2. The explosive bonding method as claimed in claim 1, wherein the supersonic explosive lies along the edge of the overlying metal body.
 3. The explosive bonding method as claimed in claim 2, wherein said subsonic explosive comprises a rectangular strip of low detonation velocity explosive which completely covers the overlapped portions of the metal bodies and said high detonation velocity explosive is in cord form and lies along the edge of the strip of low velocity explosive adjacent the edge of the overlapped metal body.
 4. The explosive bonding method as claimed in claim 1, wherein said low detonation velocity explosive has a detonation velocity on the order of 5,600 feet per second to 6,100 feet per second and said high detonation velocity explosive has a detonation velocity on the order of 22,300 feet per second to 23,600 feet per second.
 5. The explosive bonding method as claimed in claim 3, wherein said low detonation velocity explosive has a detonation velocity on the order of 5,600 feet per second to 6,100 feet per second and said high detonation velocity explosive has a detonation velocity on the order of 22,300 feet per second to 23,600 feet per second.
 6. The explosive bonding method as claimed in claim 5, wherein said overlapping metal bodies are on the order of 0.005 inches in thickness and are spaced from each other in the overlap area a distance of 0.030 inches.
 7. The explosive bonding method as claimed in claim 1, wherein the detonation velocity of the high velocity explosive is in excess of 150 percent of the sonic velocity in the metal body having the highest sonic velocity in the system.
 8. The explosive bonding method as claimed in claim 3, wherein the detonation velocity of the high velocity explosive is in excess of 150 percent of the sonic velocity in the metal body having the highest sonic velocity in the system. 